Gallagher began acting at the age of two, modeling for print advertorials in and around New York City, which eventually led to commercial work as an actor. As a toddler, he appeared in several television commercials for products such as
Tyson Foods and
Fisher-Price. When he was eight years old, he had a recurring role on the soap opera
Loving. Gallagher made his film debut in 1993 portraying Mikey Ubriacco in the film ''
Look Who's Talking Now!, and in 1995 was part of a production of A Christmas Carol on Broadway. He also starred in several television film, including Bermuda Triangle''. In 1996, Gallagher co-starred with
John Travolta in the film
Phenomenon as Al Pennamin. Later that year, he was cast as Simon Camden in
7th Heaven, which aired for eleven seasons, making it the longest-running family drama on television, and became the highest-rated series on
The WB. During hiatuses from filming, he appeared in several films, including the direct-to-video ''
Richie Rich's Christmas Wish and Little Secrets with Evan Rachel Wood. In 2003, during 7th Heaven
s eighth season, Gallagher left the show to attend college full-time. However, he returned to the series part-time during the ninth season and the tenth season, which was thought to be the final season. In late 2006, The CW renewed 7th Heaven
for an eleventh season, but Gallagher chose not to renew his contract. In 2005, Gallagher starred in and co-produced a low-budget adaptation of The Picture of Dorian Gray''. After leaving
7th Heaven, he had several roles, including serial killer Buck Winters in
Numb3rs, a murder suspect in the
CSI: Miami episode "Dangerous Son", Mark in
Boogeyman 2, Paul Shapiro in
Saving Grace, Ryan Stephenson in
Bones, Jeff Ellis in
Without a Trace, Seiji Amasawa in the English dub of
Whisper of the Heart, and Kevin Mather in
The Deep End episode "An Innocent Man". In March 2012, it was announced that Gallagher would be co-starring with
Jake Weber in
Scared of the Dark, directed by
Takashi Shimizu. Since 2002, Gallagher has been the voice of
Riku in the video game series
Kingdom Hearts. In April 2024, it was announced that Gallagher and his former co-stars,
Beverley Mitchell and
Mackenzie Rosman, would co-host the
7th Heaven rewatch podcast
Catching up with the Camdens!. ==Filmography==